It requires Tcl/Tk to be installed on your machine (http://www.tcl.tk). The editor is pretty simple. After starting "blck.tcl", you have to specify the playfield size (max. 32). In the editor you can now select tiles and place them onto the field (drag&drop works, too). When placing teleporters, switches or teleport destination (crosshair) you need to select which one (0-5). For switch destinations (0/1 tile) you also need to specifiy the "on" and "off" state of the tile.
A "right-click" on switch destination shows the tile's "on" and "off" states. With the "Export" button a small window opens showing the ASCII representation of the level and the switches. Use Copy/Paste to add them to the "level.h". The "Import" button opens also a small window, where you can Copy/Paste from the "level.h". That's it.